Custom hooks

You can provide custom hooks by placing plain JavaScript files, with .js file extension, into the hooks directory. Each file must export a hook provider object. Takomo uses the provider to initialize the actual hook.

You can use all language features available in Node 14.4.0.

Hook provider

Hook provider has the following properties:

Key	Required	Type	Description
type	yes	string	Type of the hook
init	yes	function	A function that initializes the hook with properties given in a stack group or stack configuration file. The function can be either synchronous or asynchronous, and must return an instantiated hook object.

Hook

Hook has the following properties:

Key	Required	Type	Description
execute	yes	function	A function that is invoked with an hook input object when the hook is executed. The function can be synchronous or asynchronous and must return a hook output.

Hook Input

A hook input is an object that is passed to hook's execute function. It has the following properties:

Key	Required	Type	Description
stage	yes	string	Current stack operation stage. Possible values are: before, after
operation	yes	string	Current stack operation. Possible values are: create, update, delete
status	yes	string	Current stack operation status. Possible values are: success, failed, cancelled This is defined only when the stage is after.
variables	yes	object	Mutable variables object containing command line and environment variables. The hook can modify existing variables and add new ones. After the hook is completed, the same variables object is passed to the subsequent hooks which can then access its contents. The variables are available also in the stack's template file.
ctx	yes	object	Command context object

Hook Output

A hook output is a value returned from hook's execute function. It is used to determine if the hook execution was successful and to share data between hooks. It can be either a boolean, an Error which is always considered as failure, or a detailed object with the following properties:

Key	Required	Type	Description
success	yes	boolean	A boolean determining if the hook execution was successful.
message	no	string	An informative message about the hook execution outcome.
value	no	any	A value to be exposed to other hooks.
skip	no	boolean	A boolean determining if all the remaining hooks of the current stack and the stack operation itself should be skipped.

Example

This example hook prints some debug information to the console.

Our file structure looks like this:

.
├─ stacks
│  └─ my-stack.yml
├─ hooks
│  └─ debug.js
└─ templates
   └─ my-stack.yml

The hook provider defined in hooks/debug.js looks like this:

hooks/debug.js

module.exports = {
  type: "debug",
  init: (props) => {
    console.log("Initialize debug hook")
    return {
      execute: (input) => {
        console.log("Execute debug hook!")
        console.log(`Stage:     ${input.stage}`)
        console.log(`Operation: ${input.operation}`)
        console.log(`Status:    ${input.status}`)
        console.log(JSON.stringify(props, null, 2))
        
        return {
          message: "OK",
          success: true,
          value: "Did some debugging"
        }
      }
    }
  }
}

Our custom hook is used in the stack configuration like so:

stacks/my-stack.yml

hooks:
  - name: my-hook
    type: debug

When executed, the hook exposes string "Did some debugging" in the mutable variables object.